1. Field of the Invention
The present invention relates, generally, to a diffractive thin-film piezoelectric light modulator and a method of fabricating the same. More particularly, the present invention relates to a diffractive thin-film piezoelectric light modulator, in which a lower protective layer is provided between a lower support and a lower electrode layer to increase the surface smoothness of the lower support, thereby increasing the surface smoothness of a micro-mirror, and a method of fabricating the diffractive thin-film piezoelectric light modulator.
2. Description of the Related Art
Recently, micro-machining techniques for fabricating micro-optical components, such as micro-mirrors, micro-lenses or switches, micro-optical sensors, micro-biochips, and micro-wireless communication devices, using a process of manufacturing a semiconductor device, have been developed. MEMS (Micro-Electro-Mechanical Systems), concerning the micro-machining techniques, and the devices and systems fabricated by such techniques, are regarded as rapidly growing technologies in a broad range of commercial applications.
In particular, the micro-mirror has been commercially applied to large image displays, optical signal distributors, bar-code scanners, or optical signal decay units, or research for commercialization thereof is under study.
FIG. 1 is a perspective view showing a conventional grating light modulator using electrostatic force, which is disclosed in U.S. Pat. No. 5,311,360.
As shown in FIG. 1, a light modulator 10 disclosed in U.S. Pat. No. 5,311,360 has a plurality of equally spaced-apart deformable grating elements 18, each of which includes a light-reflective planar surface and is suspended above a silicon substrate 16. Further, an insulating layer 11 is deposited on the substrate 16, after which a sacrificial silicon dioxide layer 12 is deposited.
The silicon dioxide layer 12 is partially etched in such a way that the grating elements 18 are supported on the silicon dioxide layer 12 by a nitride frame 20.
To modulate light having a single wavelength of λ0, the modulator 10 is designed so that the thicknesses of the grating elements 18 and the silicon dioxide layer 12 total one quarter of λ0.
The grating amplitude of the modulator 10, which is defined by a vertical distance d between the reflective surfaces of the grating elements 18 and the reflective surface of the substrate 16, is controlled by applying voltage between the grating elements 18 and the substrate 16.
However, since the light modulator disclosed in U.S. Pat. No. 5,311,360 uses electrostatic force for position control of the micro-mirror, the switching voltage is relatively high (about 30 V) and the relationship between the applied voltage and the displacement is not linear, therefore resulting in unreliable light control.
To overcome the above problems, thin-film piezoelectric light modulators have been proposed.
In this regard, a conventional diffractive thin-film piezoelectric light modulator is shown in FIG. 2.
As shown in FIG. 2, a conventional diffractive thin-film piezoelectric light modulator 100 includes a silicon substrate 101, a lower support 102 formed on the silicon substrate 101, lower electrode layers 103 formed on both sides of the lower support 102, piezoelectric material layers 104 formed on the lower electrode layers 103, upper electrode layers 105 formed on the piezoelectric material layers 104, and a micro-mirror 106 positioned at a central portion on the lower support 102.
In the conventional diffractive thin-film piezoelectric light modulator 100, when voltage is applied to the lower electrode layer 103 and the upper electrode layer 105, the piezoelectric material layer 104 contracts and expands to allow the lower support 102 and the micro-mirror 106 to vertically move.
However, the conventional diffractive thin-film piezoelectric light modulator 100 is disadvantageous in that because the central portions of the lower electrode layer 103, the piezoelectric material layer 104 and the upper electrode layer 105 may be over-etched when etching to form the micro-mirror 106 is conducted, the central portion of the lower support 102 may also be etched.
Thus, in the conventional diffractive thin-film piezoelectric light modulator 100, the rough surface of the central portion of the lower support 102 negatively affects the surface of the micro-mirror 106.
The micro-mirror 106 of the conventional diffractive thin-film piezoelectric light modulator 100 has low reflectivity, due to its rough surface, and hence, the light efficiency is decreased.